Method for manufacture of semiconductor bearing thin film material

ABSTRACT

A method for forming a semiconductor bearing thin film material. The method includes providing a metal precursor and a chalcogene precursor. The method forms a mixture of material comprising the metal precursor, the chalcogene precursor and a solvent material. The mixture of material is deposited overlying a surface region of a substrate member. In a specific embodiment, the method maintains the substrate member including the mixture of material in an inert environment and subjects the mixture of material to a first thermal process to cause a reaction between the metal precursor and the chalcogene material to form a semiconductor metal chalcogenide bearing material overlying the substrate member. The method then performs a second thermal process to remove any residual solvent and forms a substantially pure semiconductor metal chalcogenide thin film material overlying the substrate member.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to provisional patent application Ser.No. 60/976,406; filed on Sep. 28, 2007; commonly assigned, and of whichis hereby incorporated by reference for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

NOT APPLICABLE

BACKGROUND OF THE INVENTION

The present invention relates generally to photovoltaic materials. Moreparticularly, the present invention provides a method and structure formanufacture of semiconductor materials for photovoltaic applications.Merely by way of example, the present method and structure have beenimplemented using a zinc sulfide thin film material, but it would berecognized that the invention may be implemented using other materials.

From the beginning of time, mankind has been challenged to find way ofharnessing energy. Energy comes in the forms such as petrochemical,hydroelectric, nuclear, wind, biomass, solar, and more primitive formssuch as wood and coal. Over the past century, modern civilization hasrelied upon petrochemical energy as an important energy source.Petrochemical energy includes gas and oil. Gas includes lighter formssuch as butane and propane, commonly used to heat homes and serve asfuel for cooking. Gas also includes gasoline, diesel, and jet fuel,commonly used for transportation purposes. Heavier forms ofpetrochemicals can also be used to heat homes in some places.Unfortunately, the supply of petrochemical fuel is limited andessentially fixed based upon the amount available on the planet Earth.Additionally, as more people use petroleum products in growing amounts,it is rapidly becoming a scarce resource, which will eventually becomedepleted over time.

More recently, environmentally clean and renewable sources of energyhave been desired. An example of a clean source of energy ishydroelectric power. Hydroelectric power is derived from electricgenerators driven by the flow of water produced by dams such as theHoover Dam in Nevada. The electric power generated is used to power alarge portion of the city of Los Angeles in California. Clean andrenewable sources of energy also include wind, waves, biomass, and thelike. That is, windmills convert wind energy into more useful forms ofenergy such as electricity. Still other types of clean energy includesolar energy. Specific details of solar energy can be found throughoutthe present background and more particularly below.

Solar energy technology generally converts electromagnetic radiationfrom the sun to other useful forms of energy. These other forms ofenergy include thermal energy and electrical power. For electrical powerapplications, solar cells are often used. Although solar energy isenvironmentally clean and has been successful to a point, manylimitations remain to be resolved before it becomes widely usedthroughout the world. As an example, one type of solar cell usescrystalline materials, which are derived from semiconductor materialingots. These crystalline materials can be used to fabricateoptoelectronic devices that include photovoltaic and photodiode devicesthat convert electromagnetic radiation into electrical power. However,crystalline materials are often costly and difficult to make on a largescale. Additionally, devices made from such crystalline materials oftenhave low energy conversion efficiencies. Other types of solar cells use“thin film” technology to form a thin film of photosensitive material tobe used to convert electromagnetic radiation into electrical power.Similar limitations exist with the use of thin film technology in makingsolar cells. That is, efficiencies are often poor. Additionally, filmreliability is often poor and cannot be used for extensive periods oftime in conventional environmental applications. Often, thin films aredifficult to mechanically integrate with each other. These and otherlimitations of these conventional technologies can be found throughoutthe present specification and more particularly below.

From the above, it is seen that improved techniques for manufacturingphotovoltaic materials and resulting devices are desired.

BRIEF SUMMARY OF THE INVENTION

According to embodiments of the present invention, a method and a systemfor forming thin film semiconductor materials for photovoltaicapplications is provided. More particularly, the present inventionprovides a method and structure for forming semiconductor materials usedfor the manufacture of photovoltaic devices. Merely by way of example,the method has been used to provide zinc sulfide for photovoltaicapplication. But it would be recognized that the present invention has amuch broader range of applicability, for example, other semiconductormetal chalcogenide materials such as zinc oxide, copper sulfide, copperoxide, zinc selenide, iron sulfide, cadmium sulfide, cadmium selenide,and others may be formed.

In a specific embodiment, a method for forming a semiconductor bearingthin film material includes providing a metal precursor. The method alsoincludes providing a chalcogene precursor. The method forms a mixture ofmaterial comprising the metal precursor, the chalcogene precursor and asolvent material. In a specific embodiment, the method deposits themixture of material overlying a surface region of a substrate member andmaintains the substrate member including the mixture of material in aninert environment. The mixture of material is subjected to a firstthermal process to form a semiconductor metal chalcogenide bearing thinfilm material overlying the surface region of the substrate member. Themethod includes subjecting the substrate member including thesemiconductor metal chalcogenide bearing thin film material to a secondthermal process to remove organic compounds including residual solventmaterial to form a substantially pure semiconductor thin film materialoverlying the surface region of the substrate.

Many benefits are achieved by ways of present invention. For example,the present invention uses starting materials that are commerciallyavailable to form a thin film of semiconductor bearing materialoverlying a suitable substrate member. The thin film of semiconductorbearing material can be further processed to form a semiconductor thinfilm material of desired characteristics, such as bandgap, impurityconcentration, carrier concentration, doping, resistivity, and others.Additionally, the present method uses environmentally friendly materialsthat are relatively non-toxic. Depending on the embodiment, one or moreof the benefits can be achieved. These and other benefits will bedescribed in more detailed throughout the present specification andparticularly below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a method for forming a metalchalcogenide bearing thin film material according to an embodiment ofthe present invention.

FIG. 2 is a simplified diagram illustrating a substrate member forforming a metal chalcogenide bearing thin film material according to anembodiment of the present invention.

FIG. 3 is a simplified diagram illustrating a system for forming a metalchalcogenide bearing thin film material according to an embodiment ofthe present invention.

FIG. 4 is a simplified diagram illustrating a method for forming a metalchalcogenide bearing thin film material according to an embodiment ofthe present invention.

FIGS. 5-13 are simplified diagrams illustrating experimental resultsaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, a method and a systemfor forming semiconductor materials for photovoltaic applications isprovided. More particularly, the present invention provides a method andsystem for processing semiconductor materials used for the manufactureof photovoltaic devices. Merely by way of example, the method has beenused to provide a metal chalcogenide thin film material, for example,zinc sulfide bearing thin film material for photovoltaic application.But it would be recognized that the present invention has a much broaderrange of applicability, for example, embodiments of the presentinvention may be used to form other metal chalcogenides such as ironsulfide, copper sulfide, zinc selenide, and others, and metal oxidessuch as zinc oxide, iron oxide, copper oxide, and others.

FIG. 1 is a simplified diagram illustrating a method for forming a metalchalcogenide bearing thin film material overlying a substrate accordingto an embodiment of the present invention. The diagram is merely anexample, which should not unduly limit the claims herein. One skilled inthe art would recognize other variations, modifications, andalternatives. As shown in FIG. 1, a metal precursor 102 is provided.Also shown in FIG. 1, a chalcogene precursor 104 is provided. Thechalcogene precursor can be an organochalcogene compound in a specificembodiment. Other suitable chalcogene precursors may also be used. In aspecific embodiment, the metal precursor and the chalcogene precursorare allowed to be dispersed or dissolved in a suitable solvent 106 toform a mixture of material 108. Taking a zinc precursor and a sulfurprecursor as an example, the zinc precursor may include zinc acetate,zinc methacrylate, zinc acrylate, zinc acetylacetonate, zinc chloride,zinc nitrate, and others. In a specific embodiment, the sulfur precursorcan be an organosulfur compound such as thiourea. Other suitable sulfurprecursors may also be used. These other sulfur precursors can includethiols, thioethers, thioacetamides, thiosulfates, and others. In aspecific embodiment, the zinc precursor and the sulfur precursor areallowed to be dispersed or dissolved in a suitable solvent to form themixture of material. The solvent can be ethanol amine, methyloxy ethanolor a combination for zinc acetate and thiourea in a preferredembodiment. Other solvent/solvents may also be used depending on theembodiment.

Referring to FIG. 2, the method includes providing a substrate member202 including a surface region 204 in a specific embodiment. Thesubstrate member may be a transparent substrate such as glass, quartz,fused silica, and others in a specific embodiment. The substrate membermay also be a metal material. Examples of the metal material may includestainless steel, aluminum, nickel, and others. Alternatively, thesubstrate member can be a semiconductor material such as silicon,silicon germanium, germanium, compound III-V semiconductor such asgallium arsenide, II-VI semiconductors and others. Other substrates suchas polymers, multilayered materials, and others may also be used. Ofcourse there can be other variations, modifications, and alternatives.

Optionally, the substrate member may be first subjected to a surfacetreatment process. Such surface treatment process can include a cleaningprocess to remove contaminants and particulates. For example, thecleaning process may include wet clean using a suitable solvent followedby drying. The wet clean can include wiping the surface of the substratemember using organic solvents such as alcohols (isopropyl alcohol,ethanol, and others) or an acid clean followed by rinsing and drying. Adry cleaning process may also be used depending on the application.Alternatively, the surface of the substrate member may be subjected to aplasma process to clean or to active the surface. Of course there can beother variations, modifications, and alternatives.

In a specific embodiment, the mixture of material is dispensed 302 ontoa center region 304 of the surface region of the substrate member asshown in FIG. 3. In a specific embodiment, the mixture of material isallowed to distribute over the surface region of the substrate member toform a thickness of material overlying the surface region of thesubstrate member. As shown, the thickness of material may be formedusing a spin coating process 306. The precursor compounds provided inthe solvent may also be distributed over the surface region using adoctor blade 308. Alternatively, the mixture of material may bedeposited using other solution deposition methods such as a dip coatingprocess, a spraying process, an inkjet process, a screen printingprocess, and others. Of course one skilled in the art would recognizeother variations, modifications, and alternatives.

As shown in FIG. 4, the thickness of material 402 comprising the mixtureof material is allowed to be evenly formed overlying the substratemember. In a specific embodiment, the substrate member including thethickness of material is maintained in an inert environment 404. Theinert environment may be provided using nitrogen, argon, helium andothers, depending on the embodiment. In a specific embodiment, themixture of material is subjected to a first thermal process 406 whilebeing maintained in the inert environment. The first thermal processprovides heat energy to allow reaction between the metal precursor andthe sulfur precursor to form the metal sulfide in a specific embodiment.Again taking r zinc acetate and thiourea as precursors as an example,the first thermal process is provided at a temperature ranging fromabout 70 Degree Celsius to about 90 Degree Celsius. Depending on theembodiment, a second thermal process 502 may be provided to removeresidual organic compounds including the solvent that may remain afterthe first thermal process as shown in FIG. 5. For example, the secondthermal process is provided at a temperature of about 300 Degree Celsiusfor organic compounds such as methyloxy ethanol. As shown, asubstantially pure metal chalcogenide 504, for example zinc sulfide isformed overlying the surface region of the substrate member after thesecond thermal process. Of course there can be other variations,modifications, and alternatives.

While the invention has been described using zinc sulfide the method hasbeen used to form other semiconductor thin film metal chalcogenides, forexample, zinc selenide (ZnSe) overlying a substrate member. The methodincludes providing a zinc precursor such as zinc acetate, zincmethacrylate, zinc acrylate, zinc acetylacetonate, zinc chloride, zincnitrate, and others. The method also provides an organo selenium as aselenium precursor. In a preferred embodiment, the organo selenium canbe selenourea. Other selenium precursors may also be used. In a specificembodiment, the zinc precursor and the selenium precursor are added to asuitable solvent to form a solution mixture of precursors. As merely anexample, zinc precursor such as zinc acetate and selenium precursor suchas selenourea are provided in a solvent comprising methoxy-ethanol andethanolamine to form the solution mixture of precursors. The solutionmixture of precursors is deposited overlying a surface region of asubstrate member using techniques such as spin coating, doctor blade,inkjet, among others. In a specific embodiment, the solution mixture ofprecursors overlying the substrate member is maintained in an inertenvironment. The method then provides a first thermal process to allow areaction between zinc acetate and selenourea to form zinc selenideoverlying the substrate member. The method also includes a secondthermal process to remove any organic compounds including residualsolvents, forming a substantially pure zinc selenide thin film materialoverlying the substrate member. Of course there can be other variations,modifications, and alternatives.

FIGS. 6-13 are simplified diagrams illustrating experimental resultsaccording to an embodiment of the present invention. Referring to FIG.6, scanning electron microscope (SEM) pictures of a zinc sulfide thinfilm surface are shown. SEM picture 601 was taken at a magnification of10,000×, SEM picture 602 was taken at a magnification of 100,000×, andSEM picture 603 was taken at magnification of 250,000×. As shown, thezinc sulfide thin film has a relatively flat surface and an uniformmorphology. Of course there can be other variations, modifications, andalternatives.

FIG. 7 is a simplified diagram illustrating elemental composition of azinc sulfide thin film material deposited on a glass substrate accordingto an embodiment of the present invention. Elemental compositionestimated using Electron dispersion X-ray spectroscopy (EDX) showed thatan atomic ratio of Zn to S was approximately 1.18. Of course there canbe other variations, modifications, and alternatives.

FIG. 8 is a simplified diagram illustrating a UV-VIS absorption spectrumof the zinc sulfide thin film material according to an embodiment of thepresent invention. A corresponding transmission spectrum is illustratedin FIG. 9. As shown, the film becomes transmissive for wavelengthsgreater than about 360 nm. Of course there can be other variations,modifications, and alternatives.

FIG. 10 is a simplified plot of absorbance square as a function ofenergy in eV for the zinc sulfide thin film material according to anembodiment of the present invention. As shown, a bandgap energy for thezinc sulfide thin film material is about 3.66 eV, which is comparable tobandgap energy of bulk zinc sulfide (3.7 eV). Of course there can beother variations, modifications, and alternatives.

FIG. 11 is a simplified plot of diagram illustrating a UV-VIS absorptionspectrum of a zinc selenide thin film material overlying a glasssubstrate according to an embodiment of the present invention. Thecorresponding transmission spectrum is illustrated in FIG. 12. As shown,the film becomes transmissive for wavelengths greater than about 480 nm.Of course there can be other variations, modifications, andalternatives.

FIG. 13 is a simplified plot of absorbance square as a function ofenergy in eV for the zinc selenide thin film material according to anembodiment of the present invention. As shown, a bandgap energy for thezinc selenide thin film material is about 2.6 eV. Of course there can beother variations, modifications, and alternatives

Although the above has been illustrated according to specificembodiments, there can be other modifications, alternatives, andvariations. For example, other metal chalcogenides such as cadmiumsulfide, iron sulfide, copper sulfide, cadmium selenide, iron selenide,copper selenide may be formed using suitable respective precursormaterials. Additionally, the metal sulfide thin film material may bedoped with suitable impurities to have a desired impuritycharacteristics. It is also understood that the examples and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to personsskilled in the art and are to be included within the spirit and purviewof this application and scope of the appended claims.

1. A method for forming semiconductor bearing thin film material, themethod comprising: providing a zinc-containing precursor; providing asulfur-containing precursor; forming a mixture of material comprisingthe zinc-containing precursor, the sulfur-containing precursor and asolvent material; depositing the mixture of material overlying a surfaceregion of a substrate member, maintaining the substrate member includingthe mixture of material in an inert environment; subjecting the mixtureof material to a first thermal process to form a semiconductorzinc-sulfide containing thin film material overlying the surface regionof the substrate member; and subjecting the semiconductor zinc-sulfidecontaining thin film material to a second thermal process to form asubstantially pure semiconductor thin film material consisting of zincsulfide, wherein the zinc sulfide comprises a bandgap energy of about94.6% or greater compared to a bulk zinc sulfide film.
 2. The method ofclaim 1 wherein the solvent material is selected from the groupconsisting of ethanol, ethanolamine, methoxyethanol, tetrahydrofuran,and ethylene glycol.
 3. The method of claim 1 wherein the first thermalprocess is provided at a temperature ranging from about 80 DegreeCelsius to about 90 Degree Celsius.
 4. The method of claim 1 wherein theinert environment is provided using nitrogen, argon, or helium.
 5. Themethod of claim 1 wherein the second thermal process is provided at atemperature of about 300 Degree Celsius and higher.
 6. The method ofclaim 1 wherein the depositing step comprises a solution depositionprocess including a spin on process, a doctor blade process, a dipcoating process, a spraying process, an screen printing process, or aninkjet process.
 7. The method of claim 1 wherein the substrate member isa transparent substrate.
 8. The method of claim 7 wherein thetransparent substrate is selected from glass, fused silica, and quartz.9. The method of claim 1 wherein the substrate member is a metal. 10.The method of claim 9 wherein the substrate member is a metal selectedfrom stainless steel, aluminum, and nickel.
 11. The method of claim 1wherein the substrate member is a semiconductor material selected fromsilicon, silicon germanium, germanium, II-VI compound semiconductors,III-V compound semiconductors, and silicon on insulator.
 12. The methodof claim 1 wherein the substrate member is a multilayer material. 13.The method of claim 1 wherein the substrate member is a polymer.
 14. Themethod of claim 1 wherein the zinc precursor is selected from zincacetate, zinc methacrylate, zinc acrylate, zinc acetylacetonate, zincchloride, and zinc nitrate.
 15. The method of claim 1 wherein the sulfurprecursor is selected from thiourea, thiols, thioethers, thioaceamides,and thiosulfates.
 16. The method of claim 1 wherein the solvent materialcomprises methoxyethanol and ethanolamine.
 17. The method of claim 1wherein the zinc sulfide material is characterized by a bandgap of about3.66 eV.